Semiconductor device

ABSTRACT

According to one embodiment, a semiconductor device includes a first electrode, a first semiconductor region of a first conductivity type, a second electrode, a gate electrode, second semiconductor regions of a second conductivity type, third semiconductor regions of the first conductivity type, and a third electrode. The second electrode is provided in a plurality in second and third directions. Each second electrode opposes a portion of the first semiconductor region in the second and third directions with an insulating layer interposed. The gate electrode is provided around each second electrode. The first semiconductor region includes first regions provided respectively around the second electrodes and the second region provided around the first regions in the second and third directions. Impurity concentration of the first conductivity type in each of the first regions is higher than impurity concentration of the first conductivity type in the second region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/816,764 filed on Mar. 12, 2020 and is based upon and claims thebenefit of priority from Japanese Patent Application No. 2019-168488,filed on Sep. 17, 2019; the entire contents of which are incorporatedherein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device.

BACKGROUND

There is a semiconductor device that includes a field plate electrode(hereinbelow, called a FP electrode) to enable an increase of thebreakdown voltage or a reduction of the ON-resistance. In such asemiconductor device, it is desirable to further increase the breakdownvoltage and reduce the ON-resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a semiconductor device according to afirst embodiment;

FIG. 2 to FIG. 5 are cross-sectional views illustrating portions of thesemiconductor device according to the first embodiment;

FIG. 6A, FIG. 6B, FIG. 7A, FIG. 7B, FIG. 8A, and FIG. 8B are processcross-sectional views illustrating manufacturing processes of thesemiconductor device according to the first embodiment;

FIG. 9A to FIG. 9H are graphs illustrating characteristics ofsemiconductor devices;

FIG. 10 is a cross-sectional view illustrating a portion of asemiconductor device according to a first modification of the firstembodiment;

FIG. 11A and FIG. 11B respectively are graphs illustrating distributionsof an n-type impurity concentration ND along line A1-A2 and line B1-B2of FIG. 10;

FIG. 12A to FIG. 12C are plan views illustrating portions ofsemiconductor devices according to a second modification of the firstembodiment;

FIG. 13 is a plan view illustrating a portion of a semiconductor deviceaccording to a third modification of the first embodiment;

FIG. 14 is a plan view illustrating a portion of a semiconductor deviceaccording to a fourth modification of the first embodiment;

FIG. 15 to FIG. 17 are cross-sectional views illustrating portions of asemiconductor device according to a second embodiment; and

FIG. 18 is a cross-sectional view illustrating a portion of asemiconductor device according to a modification of the secondembodiment.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor device includes a firstelectrode, a first semiconductor region of a first conductivity type, asecond electrode, a gate electrode, a plurality of second semiconductorregions of a second conductivity type, a plurality of thirdsemiconductor regions of the first conductivity type, and a thirdelectrode. The first semiconductor region is provided on the firstelectrode and electrically connected to the first electrode. The secondelectrode opposes a portion of the first semiconductor region in asecond direction and a third direction with an insulating layerinterposed. A plurality of the second electrodes are provided in thesecond direction and the third direction. The second direction isperpendicular to a first direction from the first electrode toward thefirst semiconductor region. The third direction is perpendicular to thefirst direction and crosses the second direction. The gate electrode isprovided around each of the second electrodes. The second semiconductorregions oppose the gate electrode with a gate insulating layerinterposed, are provided respectively between the gate electrode and thesecond electrodes. The third semiconductor regions are providedrespectively on the second semiconductor regions. The third electrode isprovided on the second semiconductor regions and the third semiconductorregions and electrically connected to the second semiconductor regions,the third semiconductor regions, and the second electrodes. The firstsemiconductor region includes a plurality of first regions providedrespectively around the second electrodes in the second direction andthe third direction, and a second region provided around the firstregions. Impurity concentrations of the first conductivity type in thefirst regions are higher than an impurity concentration of the firstconductivity type in the second region.

Various embodiments are described below with reference to theaccompanying drawings.

The drawings are schematic and conceptual; and the relationships betweenthe thickness and width of portions, the proportions of sizes amongportions, etc., are not necessarily the same as the actual values. Thedimensions and proportions may be illustrated differently amongdrawings, even for identical portions.

In the specification and drawings, components similar to those describedpreviously or illustrated in an antecedent drawing are marked with likereference numerals, and a detailed description is omitted asappropriate.

In the drawings and the description recited below, the notations of n⁺,n⁻, p⁺, and p indicate relative levels of the impurity concentrations.In other words, a notation marked with “+” indicates that the impurityconcentration is relatively higher than that of a notation not markedwith either “+” or “−;” and a notation marked with “−” indicates thatthe impurity concentration is relatively lower than that of a notationwithout any mark. In the case where both a p-type impurity and an n-typeimpurity are included in each region, these notations indicate relativelevels of the net impurity concentrations after the impurities arecompensated.

In the embodiments described below, each embodiment may be performed byinverting the p-type and the n-type of each semiconductor region.

First Embodiment

FIG. 1 is a plan view illustrating a semiconductor device according to afirst embodiment.

FIG. 2 to FIG. 5 are cross-sectional views illustrating portions of thesemiconductor device according to the first embodiment.

FIG. 2 is a II-II cross-sectional view of FIG. 4 and FIG. 5. FIG. 3 is aIII-III cross-sectional view of FIG. 4 and FIG. 5. FIG. 4 is a IV-IVcross-sectional view of FIG. 2 and FIG. 3. FIG. 5 is a V-Vcross-sectional view of FIG. 2 and FIG. 3.

The semiconductor device according to the first embodiment is, forexample, a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).As illustrated in FIG. 1 to FIG. 5, the semiconductor device 100according to the first embodiment includes an n⁻-type (firstconductivity type) drift region 1 (a first semiconductor region), ap-type (second conductivity type) base region 2 (a second semiconductorregion), an n⁺-type source region 3 (a third semiconductor region), ann⁺-type drain region 4, a p⁺-type contact region 5, a drain electrode 11(a first electrode), a FP electrode 12 (a second electrode), a sourceelectrode 13 (a third electrode), and a gate pad 14.

A first direction D1, a second direction D2, and a third direction D3are used in the description of the embodiment. The direction from thedrain electrode 11 toward the n⁻-type drift region 1 is taken as a firstdirection D1. One direction perpendicular to the first direction D1 istaken as a second direction D2. A direction which is perpendicular tothe first direction D1 and crosses the second direction D2 is taken as athird direction D3. For the description, the direction from the drainelectrode 11 toward the n⁻-type drift region 1 is called “up;” and thereverse direction is called “down.” These directions are based on therelative positional relationship between the drain electrode 11 and then⁻-type drift region 1 and are independent of the direction of gravity.

As illustrated in FIG. 1, the source electrode 13 and the gate pad 14are provided at the upper surface of the semiconductor device 100. Thesource electrode 13 and the gate pad 14 are electrically isolated fromeach other. In the semiconductor device 100, a gate interconnect 15which surrounds the source electrode 13 is connected to the gate pad 14.

As illustrated in FIG. 2 and FIG. 3, the drain electrode 11 is providedat the lower surface of the semiconductor device 100. The n⁻-type driftregion 1 is provided on the drain electrode 11 with the n⁺-type drainregion 4 interposed. The n⁻-type drift region 1 is electricallyconnected to the drain electrode 11 via the n⁺-type drain region 4.

As illustrated in FIG. 2 to FIG. 5, multiple FP electrodes 12 areprovided in the second direction D2 and the third direction D3. Themultiple FP electrodes 12 are separated from each other. A gateelectrode 10 is provided around each of the FP electrodes 12. The gateelectrode 10 extends in the third direction D3 between the FP electrodes12 adjacent to each other in the second direction D2. Also, the gateelectrode 10 extends in the second direction D2 between the FPelectrodes 12 adjacent to each other in the third direction D3. The gateelectrode 10 is electrically connected to the gate interconnect 15.

As illustrated in FIG. 2, FIG. 3, and FIG. 5, the FP electrode 12opposes a portion of the n⁻-type drift region 1 in the second directionD2 and the third direction D3 with an insulating layer 12 a interposed.As illustrated in FIG. 2 and FIG. 3, multiple p-type base regions 2 areprovided on the n⁻-type drift region 1. The multiple p-type base regions2 are provided respectively between the gate electrode 10 and themultiple FP electrodes 12. The multiple n⁺-type source regions 3 and themultiple p⁺-type contact regions 5 are selectively provided respectivelyon the multiple p-type base regions 2.

Each of the p-type base regions 2 opposes the gate electrode 10 in thesecond direction D2 and the third direction D3 with a gate insulatinglayer 10 a interposed. In the semiconductor device 100, the gateelectrode 10 also opposes the multiple n⁺-type source regions 3 and aportion of the n⁻-type drift region 1 in the second direction D2 and thethird direction D3.

The source electrode 13 is provided on the n⁺-type source region 3, thep⁺-type contact region 5, the gate electrode 10, and the FP electrode12. The source electrode 13 is electrically connected to the n⁺-typesource region 3, the p⁺-type contact region 5, and the FP electrode 12.The p-type base region 2 is electrically connected to the sourceelectrode 13 via the p⁺-type contact region 5. An insulating layer isprovided between the gate electrode 10 and the source electrode 13; andthese electrodes are electrically isolated.

Operations of the semiconductor device 100 will now be described.

A voltage that is not less than a threshold is applied to the gateelectrode 10 in a state in which a voltage that is positive with respectto the source electrode 13 is applied to the drain electrode 11.Thereby, a channel (an inversion layer) is formed in the p-type baseregion 2; and the semiconductor device 100 is set to the ON-state.Electrons from the source electrode 13 pass through the channel and flowtoward the drain electrode 11. Subsequently, when the voltage applied tothe gate electrode 10 becomes lower than the threshold, the channel inthe p-type base region 2 disappears; and the semiconductor device 100 isset to the OFF-state.

When the semiconductor device 100 is switched to the OFF-state, thevoltage that is positive with respect to the source electrode 13 and isapplied to the drain electrode 11 increases. Due to the increase of thepositive voltage, a depletion layer spreads from the interface betweenthe n⁻-type drift region 1 and the insulating layer 12 a toward then⁻-type drift region 1. The breakdown voltage of the semiconductordevice 100 can be increased by the spreading of the depletion layer. Or,the ON-resistance of the semiconductor device 100 can be reduced whilemaintaining the breakdown voltage of the semiconductor device 100 byincreasing the n-type impurity concentration in the n⁻-type drift region1.

When the depletion layer spreads to the n⁻-type drift region 1, carriers(electrons and holes) that are generated by impact ionization, etc., areaccelerated inside the depletion layer; and avalanche breakdown occurs.When avalanche breakdown occurs, the electrons pass through the n⁺-typedrain region 4 and are discharged from the drain electrode 11. The holespass through the p⁺-type contact region 5 and are discharged toward thesource electrode 13.

As illustrated in FIG. 2, FIG. 3, and FIG. 5, the n⁻-type drift region 1includes multiple first regions 1 a and a second region 1 b. Themultiple first regions 1 a are provided respectively around the multipleFP electrodes 12. The second region 1 b is provided around the multipleFP electrodes 12. At least a portion of the second region 1 b ispositioned under the gate electrode 10. The n-type impurityconcentrations in the first regions 1 a are higher than the n-typeimpurity concentration in the second region 1 b and lower than thep-type impurity concentration in the p-type base region 2. Asillustrated in FIG. 2, a thickness T1 of the first region 1 a betweenthe second region 1 b and the FP electrode 12 is substantially uniformaround the FP electrode 12.

Examples of the materials of the components of the semiconductor device100 will now be described.

The n⁻-type drift region 1, the p-type base region 2, the n⁺-type sourceregion 3, the n⁺-type drain region 4, and the p⁺-type contact region 5include silicon, silicon carbide, gallium nitride, or gallium arsenideas semiconductor materials. In the case where silicon is used as thesemiconductor material, arsenic, phosphorus, or antimony can be used asthe n-type impurity. Boron can be used as the p-type impurity.

The gate electrode 10 and the FP electrode 12 include a conductivematerial such as polysilicon, etc. An impurity may be added to theconductive material.

The gate insulating layer 10 a and the insulating layer 12 a include aninsulating material such as a silicon oxide, etc.

The drain electrode 11 and the source electrode 13 include a metal suchas aluminum, copper, etc.

An example of a method for manufacturing the semiconductor device 100according to the first embodiment will now be described.

FIG. 6A to FIG. 8B are process cross-sectional views illustratingmanufacturing processes of the semiconductor device according to thefirst embodiment. FIG. 6A to FIG. 8B illustrate manufacturing processesin a cross section parallel to the first direction D1 and the seconddirection D2.

A semiconductor substrate S which includes an n⁺-type semiconductorlayer 4 s and an n⁻-type semiconductor layer 1 s provided on the n⁺-typesemiconductor layer 4 s are prepared. Openings OP are formed by removinga portion of the n⁻-type semiconductor layer 1 s. Multiple openings OPare formed in the second direction D2 and the third direction D3. Aregion 1 r is formed as illustrated in FIG. 6A along the inner surfacesof the openings OP. The n-type impurity concentration in the region 1 ris higher than the n-type impurity concentration in the n⁻-typesemiconductor layer 1 s and lower than the n-type impurity concentrationin the n⁺-type semiconductor layer 4 s.

For example, the region 1 r is formed by ion-implanting an n-typeimpurity into the inner surfaces of the openings OP. Or, an impuritylayer that includes the n-type impurity may be formed inside theopenings OP. The region 1 r is formed by diffusing the n-type impurityfrom the impurity layer into the n⁻-type semiconductor layer 1 s. Theregion 1 r may be formed by exposing the n⁻-type semiconductor layer 1 sto a plasma atmosphere of the n-type impurity. The region 1 r may beformed by epitaxially growing a semiconductor layer including the n-typeimpurity along the inner surfaces of the openings OP. Or, the region 1 rmay be formed by appropriately combining these methods.

After forming the region 1 r by any of the methods described above, aninsulating layer IL1 is formed along the inner surfaces of the multipleopenings OP and the upper surface of the n⁻-type semiconductor layer 1 sby thermal oxidation. A conductive layer that fills the multipleopenings OP is formed on the insulating layer IL1. For example, theconductive layer includes polysilicon to which an impurity is added. TheFP electrodes 12 are formed respectively inside the openings OP asillustrated in FIG. 6B by causing the upper surface of the conductivelayer to recede.

A portion of the insulating layer IL1 is removed to expose the uppersurface of the n⁻-type semiconductor layer 1 s. A trench TR whichextends in the second direction D2 or the third direction D3 is formedbetween the openings OP. The trench TR is formed to be shallower thanthe openings OP. As illustrated in FIG. 7A, an insulating layer IL2 isformed along the inner surface of the trench TR, the upper surfaces ofthe p-type base regions 2, and the upper surfaces of the FP electrodes12 by thermal oxidation. The insulating layer IL2 is formed to bethinner than the insulating layer IL1.

A conductive layer that includes polysilicon is formed on the insulatinglayer IL2; and the upper surface of the conductive layer is caused torecede. Thereby, the gate electrode 10 is formed around the upperportions of the FP electrodes 12. A p-type impurity is ion-implantedinto the upper surface of the n⁻-type semiconductor layer 1 s. Thereby,the multiple p-type base regions 2 are formed respectively between thegate electrode 10 and the upper portions of the multiple FP electrodes12. The n⁺-type source regions 3 are formed as illustrated in FIG. 7B byion-implanting an n-type impurity into portions of the p-type baseregions 2.

An insulating layer IL3 is formed on the insulating layer IL2 and thegate electrode 10. A portion of the insulating layer IL2 and a portionof the insulating layer IL3 are removed to expose the upper surfaces ofthe multiple p-type base regions 2 and the upper surfaces of themultiple FP electrodes 12. The p⁺-type contact regions 5 are formed asillustrated in FIG. 8A by ion-implanting a p-type impurity into portionsof the p-type base region 2.

A metal layer is formed on the multiple FP electrodes 12 and theinsulating layer IL3. The source electrode 13 is formed by patterningthe metal layer. The back surface of the n⁺-type semiconductor layer 4 sis polished until the n⁺-type semiconductor layer 4 s has a prescribedthickness.

Subsequently, as illustrated in FIG. 8B, the semiconductor device 100illustrated in FIG. 1 to FIG. 5 is manufactured by forming the drainelectrode 11 at the back surface of the n⁺-type semiconductor layer 4 s.

In the manufacturing processes described above, chemical vapordeposition (CVD) or sputtering can be used to form the components. Wetetching, chemical dry etching (CDE), or reactive ion etching (RIE) canbe used to remove portions of the components. Wet etching, CDE, orchemical mechanical polishing (CMP) can be used to planarize the uppersurfaces of the components or cause the upper surfaces of the componentsto recede.

Effects of the first embodiment will now be described.

As described above, when the semiconductor device 100 is switched fromthe ON-state to the OFF-state, a depletion layer spreads around each ofthe FP electrodes 12. At this time, as illustrated in FIG. 5, when adepletion layer DL having a width Wa spreads, the n⁻-type drift region 1is completely depleted between the FP electrodes 12 in the seconddirection D2 and the third direction D3.

Here, a direction that is perpendicular to the first direction D1 andcrosses the second direction D2 and the third direction D3 is taken as afourth direction D4. The angle between the second direction D2 and thefourth direction D4 is equal to the angle between the third direction D3and the fourth direction D4. A distance Di1 between the insulatinglayers 12 a adjacent to each other in the fourth direction D4 is longerthan a distance Dig between the insulating layers 12 a adjacent to eachother in the second direction D2 or the third direction D3. Accordingly,even if a depletion layer having the width Wa spreads in the fourthdirection D4, the n⁻-type drift region 1 is not depleted completelybetween the FP electrodes 12 adjacent to each other in the fourthdirection D4. The breakdown voltage of the semiconductor device 100decreases when the n⁻-type drift region 1 between the FP electrodes 12is not depleted completely.

To completely deplete the n⁻-type drift region 1 between the FPelectrodes 12 in the fourth direction D4, there is a method of reducingthe n-type impurity of the n⁻-type drift region 1. However, according tosuch a method, the electrical resistance of the n⁻-type drift region 1increases. Therefore, the ON-resistance of the semiconductor device 100increases.

For the problems described above, the n⁻-type drift region 1 includesthe multiple first regions 1 a and the second region 1 b in thesemiconductor device 100 according to the first embodiment. The multiplefirst regions 1 a are provided respectively around the multiple FPelectrodes 12. The second region 1 b is provided around the multiplefirst regions 1 a. Therefore, a length L3 of the second region 1 bbetween the FP electrodes 12 adjacent to each other in the fourthdirection D4 is longer than a length L1 of the second region 1 b betweenthe FP electrodes 12 adjacent to each other in the second direction D2.The length L3 is longer than a length L2 of the second region 1 bbetween the FP electrodes 12 adjacent to each other in the thirddirection D3.

Also, the n-type impurity concentration in the first region 1 a ishigher than the n-type impurity concentration in the second region 1 b.Accordingly, the depletion layer spreads easily in the second region 1 bcompared to the first region 1 a. Therefore, according to the firstembodiment, compared to when the n-type impurity concentration in then⁻-type drift region 1 is uniform, the n⁻-type drift region 1 betweenthe FP electrodes 12 in the fourth direction D4 is depleted easily evenwhen the length L3 is longer than the length L1 and longer than thelength L2.

Effects of the first embodiment will now be described more specificallywith reference to FIG. 9A to FIG. 9H.

FIG. 9A to FIG. 9H are graphs illustrating characteristics ofsemiconductor devices.

FIG. 9A to FIG. 9D illustrate characteristics of the semiconductordevice according to the first embodiment. FIG. 9E to FIG. 9H illustratecharacteristics of two semiconductor devices according to referenceexamples.

In the semiconductor device ref1 and ref2 according to the referenceexamples, the n-type impurity concentration in the n⁻-type drift region1 is uniform. For example, in the semiconductor device ref1, the firstregion 1 a is provided in the entire n⁻-type drift region 1. In thesemiconductor device ref2, the n-type impurity concentration in then⁻-type drift region 1 is lower than an intermediate value between then-type impurity concentration in the first region 1 a and the n-typeimpurity concentration in the second region 1 b.

FIG. 9A and FIG. 9E illustrate an n-type impurity concentration ND inthe n⁻-type drift region 1 between the FP electrodes 12 adjacent to eachother in the second direction D2. FIG. 9B and FIG. 9F illustrate anelectric field intensity E in the n⁻-type drift region 1 between the FPelectrodes 12 adjacent to each other in the second direction D2. FIG. 9Cand FIG. 9G illustrate the n-type impurity concentration ND in then⁻-type drift region 1 between the FP electrodes 12 adjacent to eachother in the fourth direction D4. FIG. 9D and FIG. 9H illustrate theelectric field intensity E in the n⁻-type drift region 1 between the FPelectrodes 12 adjacent to each other in the fourth direction D4. Thebreakdown voltage of each semiconductor device is expressed by theintegral of the electric field intensity.

In the semiconductor device ref1 as illustrated in FIG. 9E and FIG. 9G,the n-type impurity concentration in the n⁻-type drift region 1 isuniform and high. Therefore, the ON-resistance of the semiconductordevice ref1 is lower than that of the semiconductor device 100.

On the other hand, as illustrated in FIG. 9F, the electric fieldintensity in the n⁻-type drift region 1 decreases uniformly. In then⁻-type drift region 1 between the FP electrodes 12 adjacent to eachother in the fourth direction D4 as illustrated in FIG. 9H, the electricfield intensity decreases to 0. Therefore, the breakdown voltage of thesemiconductor device ref1 decreases greatly compared to thesemiconductor device 100.

In the semiconductor device ref2 as illustrated in FIG. 9F and FIG. 9H,the n⁻-type drift region 1 between the FP electrodes depletes completelyin all directions. Therefore, the breakdown voltage of the semiconductordevice ref2 is higher than the breakdown voltage of the semiconductordevice ref1. However, because the n-type impurity concentration in then⁻-type drift region 1 is uniform and low, the ON-resistance of thesemiconductor device ref2 increases greatly compared to theON-resistance of the semiconductor device 100 and the ON-resistance ofthe semiconductor device ref2.

In the semiconductor device 100 according to the first embodiment asillustrated in FIG. 9A, the n-type impurity concentration in the firstregion 1 a is higher than the n-type impurity concentration in thesecond region 1 b. Therefore, the electrical resistivity of the firstregion 1 a in the ON-state can be reduced to about the same as theelectrical resistivity of the n⁻-type drift region 1 of thesemiconductor device ref1. Thereby, the ON-resistance of thesemiconductor device 100 can be reduced more than the ON-resistance ofthe semiconductor device ref2.

Also, the second region 1 b depletes easily compared to the first region1 a. Therefore, as illustrated in FIG. 9B, the decrease of the electricfield intensity in the second region 1 b can be more gradual than thedecrease of the electric field intensity in the n⁻-type drift region 1of the semiconductor device ref1. Thereby, the breakdown voltage of thesemiconductor device 100 can be larger than the breakdown voltage of thesemiconductor device ref1.

In other words, according to the first embodiment, compared to thereference examples, it is possible to increase the breakdown voltage andreduce the ON-resistance while avoiding the large ON-resistance increaseand the large breakdown voltage decrease.

The first region 1 a may be provided around the FP electrode 12 only inthe second direction D2 and the third direction D3. In other words, thefirst region 1 a may not be provided between the drain electrode 11 andthe FP electrode 12 in the first direction D1; and the second region 1 bmay be provided at the bottom portion vicinity of the insulating layer12 a. In such a case as well, it is possible to increase the breakdownvoltage and reduce the ON-resistance because the depletion layer spreadseasily toward the fourth direction D4.

However, electrons flow also at the bottom portion vicinity of theinsulating layer 12 a when the semiconductor device 100 is in theON-state. The electrical resistance for the flow of the electrons can bereduced by providing the first region 1 a at the bottom portion vicinityof the insulating layer 12 a. In other words, the ON-resistance of thesemiconductor device 100 can be reduced further.

First Modification

FIG. 10 is a cross-sectional view illustrating a portion of asemiconductor device according to a first modification of the firstembodiment.

FIG. 11A and FIG. 11B respectively are graphs illustrating distributionsof the n-type impurity concentration ND along line A1-A2 and line B1-B2of FIG. 10.

In the semiconductor device 110 according to the first modification, then⁻-type drift region 1 further includes a third region 1 c. The thirdregion 1 c is provided between the n⁺-type drain region 4 and the firstregion 1 a, between the n⁺-type drain region 4 and the second region 1b, and between the n⁺-type drain region 4 and the FP electrode 12.

As illustrated in FIG. 11B, the n-type impurity concentration in thethird region 1 c is higher than the n-type impurity concentration in thesecond region 1 b. For example, as illustrated in FIG. 11A, the n-typeimpurity concentration in the third region 1 c is the same as the n-typeimpurity concentration in the first region 1 a. Or, the n-type impurityconcentration in the third region 1 c may be lower than the n-typeimpurity concentration in the first region 1 a.

The ON-resistance of the semiconductor device 110 can be reducedcompared to the semiconductor device 100 by providing the third region 1c having the higher n-type impurity concentration under the first region1 a, the second region 1 b, and the FP electrode 12.

By providing the third region 1 c, the breakdown voltage of thesemiconductor device 110 is reduced compared to the semiconductor device100. To adjust the reduction amount of the breakdown voltage and theON-resistance, the third region 1 c may be provided selectively betweenthe n⁺-type drain region 4 and the first region 1 a, between the n⁺-typedrain region 4 and the second region 1 b, and between the n⁺-type drainregion 4 and the FP electrode 12.

Second Modification

FIG. 12A to FIG. 12C are plan views illustrating portions ofsemiconductor devices according to a second modification of the firstembodiment.

FIG. 12A to FIG. 12C illustrate structures of a cross section passingthrough the n⁻-type drift region 1 and the FP electrode 12 parallel tothe second direction D2 and the third direction D3.

In the semiconductor devices 100 and 110, the FP electrode 12 has acircular configuration when viewed from the first direction D1.Conversely, in a semiconductor device 121 illustrated in FIG. 12A, theFP electrode 12 has a quadrilateral configuration when viewed from thefirst direction D1. In a semiconductor device 122 illustrated in FIG.12B, the FP electrode 12 has a hexagonal configuration when viewed fromthe first direction D1. In a semiconductor device 123 illustrated inFIG. 12C, the FP electrode 12 has an octagonal configuration when viewedfrom the first direction D1.

In all of these structures, the multiple first regions 1 a are providedrespectively around the multiple FP electrodes 12. The second region 1 bis provided around the multiple first regions 1 a. It is possible toreduce the ON-resistance and increase the breakdown voltage thereby. Inother words, as long as the first region 1 a and the second region 1 bare provided, the specific structure of the FP electrode 12 ismodifiable as appropriate.

Third Modification

FIG. 13 is a plan view illustrating a portion of a semiconductor deviceaccording to a third modification of the first embodiment.

FIG. 13 illustrates the structure of the semiconductor device in a crosssection passing through the n⁻-type drift region 1 and the FP electrode12 along the second direction D2 and the third direction D3.

In the semiconductor device 130 illustrated in FIG. 13, the seconddirection D2 and the third direction D3 which are the arrangementdirections of the FP electrodes 12 are not orthogonal to each other. Inthe example of FIG. 13, the angle between the second direction D2 andthe third direction D3 is 60 degrees; and the FP electrodes 12 arearranged in a staggered configuration.

When the depletion layer DL which has the width Wa spreads in thesemiconductor device 130, the n⁻-type drift region 1 between the FPelectrodes 12 is depleted in the second direction D2 or the thirddirection D3. On the other hand, in the fourth direction D4 whichcrosses the second direction D2 and the third direction D3, the n⁻-typedrift region 1 is not depleted completely even when the depletion layerhaving the width Wa spreads. Therefore, in the semiconductor device 130as well, it is effective to provide the first region 1 a and the secondregion 1 b in the n⁻-type drift region 1. By providing the first region1 a and the second region 1 b, the depletion layer spreads easily in thefourth direction D4 while suppressing the increase of the ON-resistance.It is possible to increase the breakdown voltage and reduce theON-resistance while avoiding the large ON-resistance increase and thelarge breakdown voltage decrease.

Fourth Modification

FIG. 14 is a plan view illustrating a portion of a semiconductor deviceaccording to a fourth modification of the first embodiment.

FIG. 14 illustrates the structure of a semiconductor device in a crosssection passing through the n⁻-type drift region 1 and the FP electrode12 along the second direction D2 and the third direction D3.

In the semiconductor device 140 illustrated in FIG. 14, the thickness T1in the second direction D2 of the first region 1 a between the secondregion 1 b and the FP electrode 12 is greater than a thickness T3 in thefourth direction D4 of the first region 1 a. Also, a thickness T2 in thethird direction D3 of the first region 1 a is greater than the thicknessT3.

In the semiconductor device 140, the proportion of the thickness of thefirst region 1 a to the distance Di1 between the FP electrodes 12adjacent to each other in the fourth direction D4 is small compared tothat of the semiconductor device 100. Therefore, in the semiconductordevice 140, the depletion layer spreads easily in the fourth directionD4 compared to that of the semiconductor device 100.

In the semiconductor device 100, the thickness of the first region 1 ais substantially uniform around the FP electrode 12. Therefore, thespreading of the depletion layer in the fourth direction D4 issuppressed by increasing the n-type impurity concentration in the firstregion 1 a. Conversely, in the semiconductor device 140, the thicknessof the first region 1 a in the fourth direction D4 is small. Therefore,the spreading of the depletion layer in the fourth direction D4 is notsuppressed easily even when the n-type impurity concentration in thefirst region 1 a is increased. Therefore, according to the fourthmodification, the ON-resistance of the semiconductor device 140 can bereduced further while maintaining the breakdown voltage.

Second Embodiment

FIG. 15 to FIG. 17 are cross-sectional views illustrating portions of asemiconductor device according to a second embodiment.

FIG. 15 is a XV-XV cross-sectional view of FIG. 16 and FIG. 17. FIG. 16is a XVI-XVI cross-sectional view of FIG. 15. FIG. 17 is a XVII-XVIIcross-sectional view of FIG. 15.

As illustrated in FIG. 15 to FIG. 17, the semiconductor device 200according to the second embodiment includes the n⁻-type drift region 1(the first semiconductor region), the p-type base region 2 (the secondsemiconductor region), the n⁺-type source region 3 (the thirdsemiconductor region), the n⁺-type drain region 4, the p⁺-type contactregion 5, the drain electrode (the first electrode), the FP electrode 12(the second electrode), the source electrode 13 (the third electrode),an insulating portion 20, insulating layers 21 and 22, and connectors 31to 33.

For example, the structure of the upper surface of the semiconductordevice 200 is similar to that of the semiconductor device 100illustrated in FIG. 1. As illustrated in FIG. 15, the drain electrode 11is provided at the lower surface of the semiconductor device 200. Then⁺-type drain region 4 and the n⁻-type drift region 1 are provided onthe drain electrode 11.

The insulating portion 20 is provided on a portion of the n⁻-type driftregion 1. The p-type base region 2 is provided on another portion of then⁻-type drift region 1. The n⁺-type source region 3 and the p⁺-typecontact region 5 are provided selectively on the p-type base region 2.The n⁺-type source region 3 is positioned around the insulating portion20 in the second direction D2 and the third direction D3.

The gate electrode 10 and the FP electrode 12 are provided inside theinsulating portion 20. The gate electrode 10 opposes the p-type baseregion 2 in the second direction D2 and the third direction D3 with thegate insulating layer 10 a, which is a portion of the insulating portion20, interposed.

A portion of the FP electrode 12 opposes the n⁻-type drift region 1 inthe second direction D2 and the third direction D3. Also, anotherportion of the FP electrode 12 opposes the gate electrode 10 in thesecond direction D2 and the third direction D3. A portion of theinsulating portion 20 is provided between the gate electrode 10 and theFP electrode 12. Thereby, the gate electrode 10 and the FP electrode 12are electrically isolated from each other.

An interconnect layer 16 is provided on the gate electrode 10 with theinsulating layer 21 interposed. The connector 31 is provided between thegate electrode 10 and the interconnect layer 16 and electricallyconnects the gate electrode 10 and the interconnect layer 16.

The source electrode 13 is provided on the interconnect layer 16 withthe insulating layer 22 interposed. A connector 32 is provided betweenthe FP electrode 12 and the source electrode 13 and electricallyconnects the FP electrode 12 and the source electrode 13. The connector33 is provided between the n⁺-type source region 3 and the sourceelectrode 13 and between the p⁺-type contact region 5 and the sourceelectrode 13 and electrically connects the n⁺-type source region 3 andthe p⁺-type contact region 5 to the source electrode 13. In other words,the connector 33 electrically connects the n⁺-type source region 3 andthe p⁺-type contact region 5 to the source electrode 13 at a positionwhere the interconnect layer 16 is not provided.

In the semiconductor device 200 as illustrated in FIG. 16 and FIG. 17,multiple gate electrodes 10, multiple FP electrodes 12, and multipleinsulating portions 20 are provided in the second direction D2 and thethird direction D3. The gate electrode 10 has a ring configuration whenviewed from the first direction D1. The FP electrode 12 is positioned atthe inner side of the gate electrode 10. The p-type base region 2 andthe n⁺-type source regions 3 are provided around the insulating portions20 in the second direction D2 and the third direction D3.

As illustrated in FIG. 15, multiple interconnect layers 16 are providedin the third direction D3. For example, each of the interconnect layers16 extends in the second direction D2 and is provided on the gateelectrodes 10 arranged in the second direction D2. The source electrode13 is provided on the multiple interconnect layers 16 with theinsulating layer 22 interposed.

In the semiconductor device 200 as illustrated in FIG. 17, similarly tothe semiconductor device 100, the n⁻-type drift region 1 includes themultiple first regions 1 a and the second region 1 b. Therefore,according to the second embodiment, similarly to the first embodiment,it is possible to increase the breakdown voltage and reduce theON-resistance while avoiding the large ON-resistance increase and thelarge breakdown voltage decrease.

Portions of the first regions 1 a are provided between the drainelectrode 11 and the multiple FP electrodes 12 in the first directionD1. In other words, the first regions 1 a are provided also at thebottom portion vicinities of the insulating portions 20. Therefore, theelectrical resistance of the n⁻-type drift region 1 in the ON-state canbe reduced; and the ON-resistance of the semiconductor device 100 can bereduced further.

Modification

FIG. 18 is a cross-sectional view illustrating a portion of asemiconductor device according to a modification of the secondembodiment.

FIG. 18 illustrates the structure of a cross section passing through then⁻-type drift region 1 and the FP electrode 12 parallel to the seconddirection D2 and the third direction D3.

In the semiconductor device 210 illustrated in FIG. 18, the thickness T1in the second direction D2 of the first region 1 a between the secondregion 1 b and the insulating portion 20 is greater than the thicknessT3 in the fourth direction D4 of the first region 1 a. The thickness T2in the third direction D3 of the first region 1 a also is greater thanthe thickness T3.

In the semiconductor device 210, the proportion of the thickness of thefirst region 1 a to the distance Di1 between the insulating portions 20adjacent to each other in the fourth direction D4 is small compared tothat of the semiconductor device 200. Therefore, the depletion layerspreads easily in the fourth direction D4 in the semiconductor device210 compared to the semiconductor device 200. Accordingly, according tothe modification, similarly to the fourth modification of the firstembodiment, the ON-resistance of the semiconductor device 210 can bereduced further while maintaining the breakdown voltage.

In the semiconductor device 200 or 210 according to the secondembodiment, similarly to the third modification of the first embodiment,the FP electrode 12 may have a polygonal configuration when viewed fromthe first direction D1. In such a case, for example, the gate electrode10 has a quadrilateral tubular configuration along the outer edge of theFP electrode 12.

Or, similarly to the fourth modification of the first embodiment, themultiple FP electrodes 12 may be provided in a staggered configurationin the semiconductor device 200 or 210 according to the secondembodiment. In such a case, the multiple gate electrodes 10 also arearranged similarly in a staggered configuration.

In the semiconductor device 200 or 210 according to the secondembodiment, as long as the first region 1 a and the second region 1 bare provided, the specific structures of the gate electrodes 10 and theFP electrodes 12 are modifiable as appropriate.

The relative level of the impurity concentration between thesemiconductor regions in each of the embodiments described above can beconfirmed using, for example, an SCM (scanning capacitance microscope).The carrier concentration in each semiconductor region can be regardedas being equal to the impurity concentration activated in eachsemiconductor region. Therefore, the relative level of the carrierconcentration between the semiconductor regions can also be confirmedusing the SCM. The impurity concentration in each semiconductor regioncan be measured by, for example, SIMS (secondary ion mass spectrometry).

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention. The embodiments described above can be embodiedby combining one another.

What is claimed is:
 1. A semiconductor device, comprising: a firstelectrode; a first semiconductor region provided on the first electrodeand electrically connected to the first electrode, the firstsemiconductor region being of a first conductivity type; a secondelectrode opposing a portion of the first semiconductor region in asecond direction and a third direction with an insulating layerinterposed, a plurality of the second electrodes being provided in thesecond direction and the third direction, the second direction beingperpendicular to a first direction from the first electrode toward thefirst semiconductor region, the third direction being perpendicular tothe first direction and crossing the second direction; a gate electrodeprovided around each of the second electrodes; a plurality of secondsemiconductor regions opposing the gate electrode with a gate insulatinglayer interposed, being provided respectively between the gate electrodeand the second electrodes, and being of a second conductivity type; aplurality of third semiconductor regions provided respectively on thesecond semiconductor regions, the third semiconductor regions being ofthe first conductivity type; and a third electrode provided on thesecond semiconductor regions and the third semiconductor regions andelectrically connected to the second semiconductor regions, the thirdsemiconductor regions, and the second electrodes, the firstsemiconductor region including a plurality of first regions providedrespectively around the second electrodes in the second direction andthe third direction, and a second region provided around the firstregions, impurity concentrations of the first conductivity type in thefirst regions being higher than an impurity concentration of the firstconductivity type in the second region.